This invention is generally directed to a unique development system, and more specifically, the present invention is directed to an improved apparatus for charging and transporting toner particles to a charging zone situated between a metering/charging means such as a metering charging roll and a transporting means. In one embodiment, the present invention is directed to an apparatus and process for simultaneously metering and charging insulating toner particles to a positive or negative polarity by delivering these particles with a biased rotating wire cage, or a known squirrel cage apparatus into rubbing contact with a metering/charging means, such as a metering charging roll, wherein the toner particles are further charged to either a positive or negative polarity. The squirrel cage device incorporated into the apparatus, and process described hereinafter accomplishes a number of objectives inclusive of, for example, its primary function, that is, for transporting toner particles contained in a reservoir or sump to the metering/charging roll nip present in the apparatus involved. Moreover, the squirrel cage may function in a manner to permit the application of charges to the toner particles contained in the sump in view of the triboelectric relationship between the wires of the brush means and the toner particles.
In addition, with the apparatus of the present invention there is provided a metered uniform amount of toner particles to the charging nip; and further, the apparatus of the present invention enables an environmentally insensitive system substantially free of the matting and toner caking problems associated with known brush development methods.
The development of images by numerous methods, including electrostatographic means is well known. In these systems, toner particles are deposited on an electrostatic latent image contained on an insulating surface such as selenium, using for example, cascade development, magnetic brush development, powder cloud development, touchdown development, and other development systems. Generally in these systems two component developer compositions are selected for development, that is compositions containing toner particles and carrier particles. As it is known that there are a number of disadvantages associated with two component systems, including additional costs and processing equipment, there has been considerable effort directed to designing systems which utilize toner particles only. Generally, these systems allow the elimination of a developer reservoir, a toner dispenser, and a toner concentration control means.
Single component development systems are also known, that is, developer compositions comprised of toner resin particles only. The single component imaging devices currently in use generally consume conductive toner particles whereby imagewise toner deposition onto the imaging member is obtained by induction toner charging. Electrostatic transfer of conductive toner particles to plain paper is, however, usually inefficient as, for example, the charge of the toner particles can be reversed by induction charging with plain conductive paper. Electrophotographic systems using conductive single component toner particles therefor usually require a special overcoated paper to achieve electrostatic transport. Moreover, in single component development systems containing conductive toner particles it is difficult to control undesirable background, and background suppression cannot be achieved as the toner particles are inductively charged, and deposited on the image bearing members, which is not the situation in two component development systems wherein the control of background development is accomplished by an electrostatic force acting on the triboelectrically charged toner particles causing such particles to be directed away from the imaging member.
There is disclosed in U.S. Pat. No. 3,900,002 development systems for developing latent electrostatic images which include a rotating fur brush, the purpose of which is to deliver toner particles to the imaging member. As illustrated in FIG. 1 of this patent, a cylindrical applicator, such as a natural fur brush, is selected for incorporation into the apparatus. A similar disclosure is presented in U.S. Pat. No. 3,929,098 wherein there is selected for electrostatic development a brush contained in a developer sump, which brush transfers toner particles to a donor roll. Particles contained on the donor roll are subsequently provided to the photoreceptor imaging member.
Also, there is disclosed in U.S. Pat. No. 3,638,613 a developer apparatus wherein a transfer or donor roll triboelectrically attracts to its surface toner particles contained in a sump or reservoir. Apparently, the fur brush is used for the purpose of removing toner from the transfer or donor roll and depositing such toner particles upon a charged surface where the image contained thereon is rendered visible.
In addition, there is illustrated in U.S. Pat. No 4,481,903 an apparatus for developing electrostatic latent images wherein there is selected, for example, two brushes which rotate in a toner reservoir and are then contacted with screens to create a toner cloud, reference column 3, beginning at line 21, and FIGS. 1 to 4; while U.S. Pat. Nos. 4,330,193 and 4,352,552 illustrate development systems with rolls of magnetized slats which pick up toner from a reservoir to enable the formation of a magnetic brush and U.S. Pat. No. 4,480,905 illustrates a dual roller structure with a single central trimming blade, and more specifically an electronic printing method wherein there is selected a development unit with a plurality of developing rolls, see column 2, beginning at line 33. Also of interest is German Publication No. 2,429,020 directed to a developer wherein there is selected a hopper with a cylinder which contains a stirrer to prevent the toner utilized from settling. Apparently, the toner powder flows through a rotating spout into a u-shaped trough which fits around a ribbed roller, see the Abstract of the Disclosure.
Recently, there has been developed an efficient, economical, simple process and apparatus for the development of latent electrostatic images with single component development systems wherein insulative, nonmagnetic, or color toner particles are appropriately charged and there is obtained two component image quality utilizing a single component development apparatus. In this system, as detailed hereinafter, and as described in U.S. Pat. No. 4,459,009, the disclosure of which is totally incorporated herein by reference, there is selected a charging roll means which simultaneously meters and charges toner particles. A donor electrode serves to transport the toner particles, which electrode can be comprised of numerous suitable materials including, for example, aluminized Mylar overcoated with a polymer containing carbon black.
There is also described in U.S. Pat. No. 4,505,573 a transporting means for insulating toner particles comprised of a suitable substrate and a coating thereover of a low surface energy, wear resistant material. More specifically, there is disclosed in this patent an insulating toner transporting system comprised of a substrate, and a coating of a fluoropolymer. The improved toner transporting means of the patent are particularly useful in an apparatus for charging toner particles comprised in operative relationship of a means for charging insulating toner particles and a means for transporting insulating toner particles, wherein the means for charging the means for transporting insulating toner particles for transporting are biased to a predetermined potential. Accordingly, in one embodiment, the invention of the referred to patent is directed to an apparatus for charging insulating toner particles, which apparatus is comprised in operative relationship of a means for charging insulating toner particles and a means for transporting insulating toner particles, the means for charging and the means for transporting being biased to a predetermined potential wherein the transporting means contains thereover a mixture of a fluoropolymer coating, and conductive particles such as carbon black.
Moreover, illustrated in a copending application U.S. Ser. No. 560,691, is an apparatus for charging insulating toner particles, which apparatus is comprised in operative relationship of a means for charging insulating toner particles, and a means for transporting insulating toner particles, the means for charging and the means for transporting being biased to a predetermined potential; and wherein there is selected, for example, a brush means for transporting the toner particles from a developer sump to the charging nip. The invention of the present application is similar to the apparatus as illustrated in the aforementioned application with the exception that, for example, there is selected for the present invention a squirrel cage for the transportation of the toner particles. While the aforementioned apparatus disclosed is suitable for its intended purposes, there may be disadvantages associated with the utilization of brush fibers inclusive of, for example, fiber weaving; and further, the fibers over a period of time are fractured and undesirably added to the developer material present in the sump, disadvantages overcome by the apparatus of the present invention. Moreover, in some situations with brush systems, particularly with high humidity conditions, that is humidities above 70 percent, there is a tendency for the toner particles to be retained between the brush bristles thereby reducing the efficiency of the toner particles to be delivered to the nip for charging which is not the situation with the apparatus of the present invention.
Although apparatuses similar to those of the present invention are known, there is a need for improved systems. Specifically, for example, there is a need for the transportation of a specific amount of toner particles to a toner transporting means present in some of the aforementioned apparatuses. There is also a need for an improved process and apparatus wherein the toner particles are transported by an assembly of wires, or a squirrel cage. Furthermore, there is a need for the rapid, and consistent collection of toner particles from a developer sump, and the direction of these particles to a charging nip present between a charging means and a toner transporting means. Moreover, there is a need for electrostatographic imaging apparatuses, and methods having incorporated therein the squirrel cage device of the present invention. Additionally, there is a need for apparatuses and processes wherein single component toners can be transported to a charging nip without the undesirable formulation of agglomerates, and wherein the resulting apparatus can be adjusted to enable the utilization of particular toner formulations, including color toners.